Police have also linked the suspect to a threat to an unspecified Northside Independent School District elementary school last week that prompted parents to pull nearly a third of students from classes across districts throughout the county.

The statement did not make clear why no one had been arrested.

School districts on Thursday afternoon reported having received another email threatening a mass school shooting at Madison High.

Police officials said Thursday that investigations into previous incidents indicate that the threat seems to have come from a person out of state who is incapable of immediately carrying them out.

“While we understand the need for San Antonio parents to feel their children are safe, we are confident that this person's lack of immediate ability to carry these threats out has been established and still continues to be the case,” the SAPD release said.

School district officials did not specify what time they got the email Thursday or whether it prompted any lockdowns.

Northside ISD spokesman Pascual Gonzalez said their high schools got the “threatening” note. They forwarded it to SAPD and also informed officials at North East ISD, which includes Madison.

NEISD superintendent Brian Gottardy sent a message to parents and staff saying that the threat made “reference to a mass shooting at an unspecified time.”

“I have spoken with San Antonio Police Chief William McManus, who continues to work with the FBI to track down this individual,” Gottardy wrote. “He assures me this threat, like the one last week, is not credible.”

Gottardy said SAPD told him no other information can be shared. He added that the NEISD Police Department, along with other local law enforcement agencies, will continue to have an increased presence at Madison High School. New security procedures, such as the use of clear or mesh backpacks, remain in effect only at Madison.

This is the third scare for Madison this week. On Monday, Madison sophomore Brendan Tarwater, 17, was arrested after he allegedly brought two loaded pistols, a loaded assault rifle and a 12-inch knife to school, forcing a lockdown.

The next day, a Judson High student sent a text message to a Madison senior implying that she was at Madison with a gun, police said. Chelsea Marie Hill, 17, was arrested Wednesday and charged with making a terroristic threat.